Buckling waves in aluminum on a polyimide sea: In situ analysis towards a reliable design strategy for stretchable electronics

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Silk Vascular Grafts with Optimized Mechanical Properties for the Repair and Regeneration of Small Caliber Blood Vessels

As the incidence of cardiovascular diseases has been growing in recent years, the need for small-diameter vascular grafts is increasing. Considering the limited success of synthetic grafts, vascular tissue engineering/repair/regeneration aim to find novel solutions. Silk fibroin (SF) has been widely investigated for the development of vascular grafts, due to its good biocompatibility, tailorable biodegradability, excellent mechanical properties, and minimal inflammatory reactions. In this study, a new generation of three-layered SF vascular scaffolds has been produced and optimized. Four designs of the SILKGraft vascular prosthesis have been developed with the aim of improving kink resistance and mechanical strength, without compromising the compliance with native vessels and the proven biocompatibility. A more compact arrangement of the textile layer allowed for the increase in the mechanical properties along the longitudinal and circumferential directions and the improvement of the compliance value, which approached that reported for the saphenous and umbilical veins. The higher braid density slightly affected the grafts' morphology, increasing surface roughness, but the novel design mimicked the corrugation approach used for synthetic grafts, causing significant improvements in kink resistance

Combination of Acoustic Methods and the Indentation Technique for the Measurement of Film Properties

New techniques are continuously being developed to produce films and thin films, whose properties typically depend on the preparation process, and can be significantly different from those of the material in bulk form. The characterization of thin layers remains an open issue. A precise knowledge of the mechanical properties is crucial in several cases, and is of general interest. A full mechanical characterization includes the determination of both the elastic properties, which characterize the reversible deformations, and the properties which characterize the reversible behaviour. In most cases the elastic behaviour can be completely characterized by the elastic moduli, or equivalently by the components of the elastic tensor. It is well known that also in the simplest case, the homogeneous isotropic continuum, the elastic stiffness cannot be characterized by a single parameter, but needs two independent parameters; in the case of anisotropic solids the number of independent parameters further increases. The inelastic behaviour is typically more complex. Among the methods to perform the mechanical characterization, a specific class exploits vibrations of acoustic nature as a probe of the material behaviour. These methods are non destructive, and involve only elastic strains; therefore, they are intrinsically unable to give indications about any inelastic behaviour. On the other hand, due to the complete absence of inelastic strains, the relationship between the raw measurement results and the stiffness parameters can be more straightforward, and less subjected to uncertainties or to spurious effects, possibly allowing better accuracies. The mechanical characterization of supported films typically requires specific methods. The most widespread technique is indentation, for which a specific standard exists, and which induces both elastic and inelastic strains: It supplies significant information about irreversible deformation, but the extraction of the information concerning the elastic behaviour is non trivial, and typically leads to a single parameter, usually referred to as 'indentation modulus'. If a reasonable assumption about the value of Poisson???s ratio is available, a value of Young modulus can be derived, which obviously depends on the reliability of the adopted assumption. In the case of films, since the nano and micro-structure can be different from that of bulk samples, a well grounded assumption about the value of Poisson???s ratio might be not available. It is also well known that, when supported films are measured, care must be exercised to avoid the influence of the substrate properties. Methods which exploit acoustic vibrations have been developed also for supported films. Acoustic properties depend on stiffness and inertia; therefore, as it happens for bulky samples, acoustic methods require a value of mass density, independently measured. However in acoustic methods the intrinsic absence of inelastic strains makes the derivation of the stiffness parameters less subjected to spurious effects, and less dependent on specific modelling assumptions. Among the techniques based on acoustic excitations, the so called laser ultrasonics techniques rely on impulsive, therefore broadband, excitation, while quantitative acoustic microscopy relies on monochromatic excitation. In the detection of vibrational excitations, substantial advantages are offered by light, a contact-less and inertia-less probe; such advantages are particularly relevant in the measurement of films and small structures. They are exploited by Brillouin spectroscopy, which relies on Brillouin scattering: the inelastic scattering of light by acoustic excitations. Brillouin spectrometry relies on spontaneous thermal excitation, which has a small amplitude, but has the broadest band, allowing access to the GHz and multi GHz band. For all these methods, the outcome is the measurement of the propagation velocity of one or more acoustic modes. If sufficient information is gathered, a full elastic characterization can be achieved by purely vibrational means, if an independent value of the mass density is available. However, a complete elastic characterization by only acoustic means is not always achievable. The results of acoustic methods and of indentation can therefore be combined, with the purpose to obtain a complete elastic characterization, not achievable by each of the techniques alone. This can be particularly useful in the case of new materials or of films of unconventiona structures, for which a reliable assumption about the value of Poisson???s ratio, needed by indentation, is not available. And the combination of techniques anyhow offers a useful cross-check among techniques based on completely different principles. This chapter is devoted to this combination of indentation with acoustic techniques, namely quantitative acoustic microscopy and Brillouin spectroscopy

Buckling waves in aluminum on a polyimide sea: In situ analysis towards a reliable design strategy for stretchable electronics

‘Stretchable electronics’ refers to highly deformable devices in which compliant polymeric substrates support micron-size sensor units; these may provide spatially distributed measurements over complex surfaces. Stretchable sensors have opened new perspectives and applications in many fields, among which biomedicine is one of the most promising: instrumentation for tools which need to withstand significant bending or stretching during service has been demonstrated via balloon catheters and implantable patches, enabling a totally new generation of smart devices. Stretchability and bendability of such systems are achieved by selecting a compliant substrate for the sensing units and by granting sufficient deformability to the electrical interconnects. The results of this study provided an insight into the local mechanics involved in the onset of the delamination and buckling in S-shape deformable interconnects. In particular, a correlation was found between the interface failure phenomena and the geometrical parameters that define the design of deformable interconnects, allowing the identification of unexpected drawbacks related to specific S-shape design features

Micro-CT imaging and finite element models reveal how sintering temperature affects the microstructure and strength of bioactive glass-derived scaffolds

: This study focuses on the finite element simulation and micromechanical characterization of bioactive glass-ceramic scaffolds using Computed micro Tomography ([Formula: see text]CT) imaging. The main purpose of this work is to quantify the effect of sintering temperature on the morphometry and mechanical performance of the scaffolds. In particular, the scaffolds were produced using a novel bioactive glass material (47.5B) through foam replication, applying six different sintering temperatures. Through [Formula: see text]CT imaging, detailed three-dimensional images of the scaffold's internal structure are obtained, enabling the extraction of important geometric features and how these features change with sintering temperature. A finite element model is then developed based on the [Formula: see text]CT images to simulate the fracture process under uniaxial compression loading. The model incorporates scaffold heterogeneity and material properties-also depending on sintering temperature-to capture the mechanical response, including crack initiation, propagation, and failure. Scaffolds sintered at temperatures equal to or higher than 700 [Formula: see text]C exhibit two-scale porosity, with micro and macro pores. Finite element analyses revealed that the dual porosity significantly affects fracture mechanisms, as micro-pores attract cracks and weaken strength. Interestingly, scaffolds sintered at high temperatures, the overall strength of which is higher due to greater intrinsic strength, showed lower normalized strength compared to low-temperature scaffolds. By using a combined strategy of finite element simulation and [Formula: see text]CT-based characterization, bioactive glass-ceramic scaffolds can be optimized for bone tissue engineering applications by learning more about their micromechanical characteristics and fracture response

Anisotropic Mechanical Response of Bovine Pericardium Membrane Through Bulge Test and In-Situ Confocal-Laser Scanning

In this work, we present a new experimental setup for the assessment of the anisotropic properties of Bovine Pericardium (BP) membranes. The chemically fixed BP samples have been subjected to a bulge test with in situ confocal laser scanning at increasing applied pressure. The high resolution topography provided by the confocal laser scanning has allowed to obtain a quantitative measure of the bulge displacement; after polynomial fitting, principal curvatures have been obtained and a degree of anisotropy (DA) has been defined as the normalized difference between the maximum and minimum principal curvatures. The experiments performed on the BP membranes have allowed us to obtain pressure-displacement data which clearly exhibit distinct principal curvatures indicating an anisotropic response. A comparison with curvatures data obtained on isotropic Nitrile Buthadiene Rubber (NBR) samples has confirmed the effectiveness of the experimental setup for this specific purpose. Numerical simulations of the bulge tests have been performed with the purpose of identifying a range of constitutive parameters which well describes the obtained range of DA on the BP membranes. The DA values have been partially validated with biaxial tests available in literature and with suitably performed uni-axial tensile tests

Mechanical Properties of Robocast Glass Scaffolds Assessed through Micro-CT-Based Finite Element Models

In this study, the mechanical properties of two classes of robocast glass scaffolds are obtained through Computed micro-Tomography (micro-CT) based Finite Element Modeling (FEM) with the specific purpose to explicitly account for the geometrical defects introduced during manufacturing. Both classes demonstrate a fiber distribution along two perpendicular directions on parallel layers with a (Formula presented.) tilting between two adjacent layers. The crack pattern identified upon compression loading is consistent with that found in experimental studies available in literature. The finite element models have demonstrated that the effect of imperfections on elastic and strength properties may be substantial, depending on the specific type of defect identified in the scaffolds. In particular, micro-porosity, fiber length interruption and fiber detaching were found as key factors. The micro-pores act as stress concentrators promoting fracture initiation and propagation, while fiber detachment reduces the scaffold properties substantially along the direction perpendicular to the fiber plane.publishedVersionPeer reviewe

Calibración y validación de un modelo de crecimiento para alfalfa (Medicago sativa L.)

En el presente trabajo se modificó un modelo de crecimiento generado por McCall y Bishop-Hurley para pasturas compuestas de gramíneas templadas perennes (Modelo McCall). El objetivo fue desarrollar un modelo de crecimiento capaz de representar el crecimiento aéreo de pasturas de alfalfa (Modelo Alfalfa) sujetas a diferentes condiciones ambientales y de manejo de la defoliación. Se trabajó con pasturas puras de alfalfa sin reposo invernal en la región central de Argentina (localidades de Manfredi, Rafaela, Susana, Marcos Juárez y Paraná). En la etapa de calibración se realizaron modificaciones para representar el crecimiento de pasturas de alfalfa que crecieron sin limitantes hídricas y nutricionales y de pasturas sometidas a distintas frecuencias de defoliación. Se modificó: 1) la relación entre temperatura media diaria del aire y la eficiencia de uso de la radiación solar global para crecimiento aéreo (parámetro α); 2) la ecuación que considera la importancia de las reservas en raíz utilizadas por las plantas durante el rebrote; y 3) el parámetro α para simular pasturas sujetas a defoliaciones de distinta frecuencia. En la etapa de validación, se observó que el Modelo Alfalfa representó adecuadamente variaciones en crecimiento asociadas tanto a variaciones en la disponibilidad de agua como a variaciones en el manejo de la defoliación. Se concluye que el Modelo Alfalfa es capaz de representar los cambios en el crecimiento causado por variaciones en los principales factores bióticos (defoliación) y abióticos (clima) del ambiente.A model originally developed by McCall and Bishop-Hurley to predict the growth of temperate perennial grasses (Modelo McCall) was modified. The aim was to develop a model capable to describe the aboveground growth of alfalfa pastures (Modelo Alfalfa) subjected to several climate and defoliation conditions. We used winter-active alfalfa pastures growing at a central region of Argentina (cities of Manfredi, Rafaela, Susana, Marcos Juárez and Paraná). Modifications realized at calibration step were made to represent the growth of alfalfa pure stands growing under non limiting conditions (i.e. irrigated and fertilized pastures) and that of pastures subjected to different defoliation frequencies. We modified: 1) the relationship between mean air daily temperature and solar radiation use efficiency (parameter α); 2) the equation taking account the use root reserves during a regrowth; and 3) parameter α to simulate pastures subjected to contrasting defoliation frequencies. At the validation step, we observed that Modelo Alfalfa adequately describe changes in aerial growth associated to variations in both, water availability and defoliation management. It was concluded that the Modelo Alfalfa is capable of representing the variations in growth caused by variations of mains biotic (defoliation) and non-biotic (climate) environmental factors.EEA BalcarceFil: Berone, German Dario. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Balcarce; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; ArgentinaFil: Di Nucci, Elena. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Paraná; ArgentinaFil: Fernández, H. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Balcarce; ArgentinaFil: Gastaldi, Laura Beatriz. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; ArgentinaFil: Mattera, Juan. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Pergamino; ArgentinaFil: Spada, María del Carmen. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Manfredi; Argentin

Effect of initial levothyroxine dose on neurodevelopmental and growth outcomes in children with congenital hypothyroidism

We designed a multicentre open prospective randomized trial to evaluate the risk-benefit profile of two different initial treatment schemes with levothyroxine (L-T4), 10-12.5 μg/kg/day vs 12.6-15 μg/kg/day, on growth and neurodevelopmental outcomes in children with congenital hypothyroidism (CH) detected by neonatal screening to identify the best range dose to achieve optimal neurocognitive development

Development of biodegradable magnesium alloy stents with coating

Biodegradable stents are attracting the attention of many researchers in biomedical and materials research fields since they can absolve their specific function for the expected period of time and then gradually disappear. This feature allows avoiding the risk of long-term complications such as restenosis or mechanical instability of the device when the vessel grows in size in pediatric patients. Up to now biodegradable stents made of polymers or magnesium alloys have been proposed. However, both the solutions have limitations. The polymers have low mechanical properties, which lead to devices that cannot withstand the natural contraction of the blood vessel: the restenosis appears just after the implant, and can be ascribed to the compliance of the stent. The magnesium alloys have much higher mechanical properties, but they dissolve too fast in the human body. In this work we present some results of an ongoing study aiming to the development of biodegradable stents made of a magnesium alloy that is coated with a polymer having a high corrosion resistance. The mechanical action on the blood vessel is given by the magnesium stent for the desired period, being the stent protected against fast corrosion by the coating. The coating will dissolve in a longer term, thus delaying the exposition of the magnesium stent to the corrosive environment. We dealt with the problem exploiting the potentialities of a combined approach of experimental and computational methods (both standard and ad-hoc developed) for designing magnesium alloy, coating and scaffold geometry from different points of views. Our study required the following steps: i) selection of a Mg alloy suitable for stent production, having sufficient strength and elongation capability; ii) computational optimization of the stent geometry to minimize stress and strain after stent deployment, improve scaffolding ability and corrosion resistance; iii) development of a numerical model for studying stent degradation to support the selection of the best geometry; iv) optimization of the alloy microstructure and production of Mg alloy tubes for stent manufacturing; v) set up, in terms of laser cut and surface finishing, of the procedure to manufacture magnesium stents; vi) selection of a coating able to assure enough corrosion resistance and computational evaluation of the coating adhesion. In the paper the multi-disciplinary approach used to go through the steps above is summarized. The obtained results suggest that developed methodology is effective at designing innovative biomedical devices